The invention relates to a driving arrangement for a record carrier in the form of tape, comprising a driven shaft and driving the record carrier, and a pressure roller having a high surface friction coefficient, the tape-like record carrier being passed between shaft and roller.
Driving a record carrier in the form of tape having a smooth surface, for example a magnetic tape, is usually performed by means of friction between two shafts or small drums, one shaft or drum being the element driving the record carrier, the other shaft or drum being the pressure element producing the counter pressure required for driving the record carrier. The first mentioned shaft or drum has a surface which is of a highest possible smoothness and, consequently, of a lowest possible friction, at least in the area where it contacts the record carrier. This smooth surface is necessary to ensure uniform travel of the record carrier perpendicularly to its longitudinal axis, which is necessary for the tone quality. Therefore, the drive shaft or small drum is denoted the capstan and the second shaft or small drum the pressure roller.
As known, however, the smooth surface of the capstan has drawbacks which are predominantly caused by the slip which is produced when the capstan must be rapidly brought to a high speed of rotation. This is, for example, the case when tape recorders are operated in the fast mode. This slip is also annoying with smooth tape-like record carriers which are used in data recorders in accounting machines and which are transported in the so-called start-stop mode.
To avoid this drawback it has been proposed to coat not only the pressure roller, but also the capstan itself with a friction layer (see, for example, IBM Technical Disclosure Bulletin, Vol. 11. No. 2, July 1968). As a result thereof the record carrier may indeed be brought relatively rapidly to the desired tape speed, but this is done at the expense of the uniform travel perpendicularly to the longitudinal axis of the record carrier as is required for high tone quality. The reason is the rapid wear of the soft surfaces of the capstan and the pressure roller, and the dependence of the layer properties on the ambient humidity.